We have a 2011 Cougar High Country 299RKS. We love it but there have been some things we've needed/wanted to do with it. For one thing in 2011 they didn't even offer a 50amp version so we are stuck with one A/C. We added a Fantastic Fan in the B/R but I would have preferred an A/C up there. I switched to 16" wheels/tires but that's personal preference. The cabinet floors in the pantry busted through from the weight of canned goods, etc, and so I rebuilt those. I think most of the issues with the unit are common with many trailers at this price level.
We do love ours and have over 15,000 miles of use on it.
We just suffered a break in our black water holding tank that I am in the midst of repairing. Don't really know who's fault that is. While I've got the whole bottom of the trailer off I am upgrading the cheezy 1/8" insulation to 1" rigid insulation board. I do help that helps keep the trailer warmer/cooler but we'll see.